I am rather disappointed with the HOYA 82 UV IR filter on the 16-35. There is a very clear green color cast in the corners.

I just researched that and decided against buying a combined (and convenient) uv+ir-blocker for my 17-40L - the filter doesn't work on wide angle but only with 35mm+ for the reasons you just experienced - the angle of the light entering is too different and results in color shifts. If you want to block IR with uwa, you need a dedicated hot mirror filter.

A thought does occur, do you really need extra IR blocking on top of what's in the camera body already?

For stills, afaik ir blocking with a filter only makes sense for long time exposures with a nd filter to counter the loss of contrast by ir pollution. But as I wrote above, the "cheaper" ir/uv unfortunately doesn't work with uwa - and stacking filters probably wouldn't either, so the only way is a very expensive combined ir/nd filter like from Tiffen.

I am rather disappointed with the HOYA 82 UV IR filter on the 16-35. There is a very clear green color cast in the corners.

At 205$, this hurts.

If spending $205 on a filter that produces green color cast in the corner hurts, imagine the Nikon D800 (costing around $3000) producing green "cast" cross the entire image. One can easily remove the Hoya filter and not have the green case at all but with D800 you have no choice but to deal with it in PP